// Press Shift twice to open the Search Everywhere dialog and type `show whitespaces`,
// then press Enter. You can now see whitespace characters in your code.
public class Main {
    public static void main(String[] args) {
        ADBoard adBoard = new ADBoard();
        adBoard.show();
        adBoard.setAdvertisement(new BlackLandCorp());
        adBoard.show();
        adBoard.setAdvertisement(new WhiteCloudCorp());
        adBoard.show();
    }
}